It has been proposed to provide foam-rubber balls or other cleaning particles in a main stream of fluid traversing a tube-bundle heat exchanger for cleaning the tubes automatically during the heat-exchange process, thereby eliminating any downtime for such cleaning. It has also been suggested that these particles can be removed from the main stream and recirculated to the latter upstream of the heat exchanger for efficient operation. A device utilizing this self-cleaning technique is described, for example, in U.S. Pat. No. 3,021,117.
A conventional system for recovering the cleaning elements from the main stream traversing a tube-bundle heat exchange can comprise a housing or duct having a sieve (separating sieve) inclined to the axis of the housing and traversed by the fluid. The particles or cleaning elements collect upon this sieve and may be carried away by a collecting tube for reuse.
In the conventional structure of this type, the sieve can be a grate formed by transversely spaced parallel bars and can have a generally ellipsoidal boundary where the sieve meets the wall of the duct or housing. In general, the collecting tube is a radially extending structure which is provided at the low point of the ellipsoidal boundary of the separating sieve to collect the particles which pass downwardly toward this low point.
In practice, however, this system is found to have problems. For example, since the separating seive lies in a plane to the cylindrical housing which can have a vertical axis, the intersection between this plane and the wall of the cylindrical housing or duct defines a wedge or taper so that the passage for the particles has a continuously decreasing cross section to the low point mentioned previously. Because of this configuration, the particles tend to jam together and to block collection of the particles in the collecting tube. Once some particles begin to block the mouth of the collecting tubes, it is necessary to terminate operations until the blockage can be cleared.